The idea of valuing nature’s services to people is not new. In 1937, Franklin Delano Roosevelt referred to natural resources as our “permanent capital,” a budget that the country was spending down faster than it could replenish. Certainly FDR was not the first to see the critical link between sustaining nature’s resources and our continued growth.

In recent decades, an increasing number of companies, governments and organizations have been thinking seriously about this complex issue of sustainability. They have developed increasingly innovative ways to quantify and assess the value of nature’s services—our natural capital—so that businesses and governments can incorporate nature in their development decisions.

The Natural Capital Project, for example—since its founding in 2006—has helped dozens of public agencies and companies assess the value they derive from lands, waters, oceans and other living ecosystems. Roosevelt described these assets as “permanent.” Our actions will determine that.

Unfortunately, this vital work of valuing nature’s services has not kept pace with the speed of global development. As economies grow, leaders in government and industry make decisions every day that either can enhance or deplete our natural capital for decades to come. And once these assets are gone, they are extremely difficult—if not impossible—to bring back. If we expect these choices to be sustainable, businesses and governments must be able to accurately assess nature’s full value, and—like any other critical asset—make the necessary investments to protect it.

The world’s rapidly growing cities have the opportunity to play a lead role in making this happen, using the unique development challenges of this explosive growth to mainstream investments in natural capital and accelerate sustainability globally.

This is an all-hands-on-deck moment for engineers, developers, urban planners, community leaders, ecologists and investors.

Today, half of the world’s people live in cities. By 2050, three out of four people will be urban citizens. This rapid growth is straining the infrastructure that makes cities livable, including roads, energy facilities, water treatment plants, reservoirs, sewers, levees, dams, seawalls and breakwaters.

By current estimates, the world’s cities will need to invest $5 trillion in upgrading their infrastructure by 2030 just to keep pace with growth.

"The explosive growth of urban areas may be our best opportunity for investing in natural capital."

This investment challenge creates an opportunity to demonstrate the cost-effective and flexible role that nature can play alongside—or, in some cases as an alternative to—the menu of traditional choices for managing water delivery, providing storm and flood protection, improving air and water quality, providing energy and supporting health.

This natural, or “green,” infrastructure is a vital component of a city’s overall infrastructure. And it provides other benefits that many engineered solutions can’t provide, such as recreation, tourism and an improved quality of life for city residents.

We are beginning to see progress:

Philadelphia is investing in more urban green spaces to absorb and filter run-off and help manage its costly storm water challenges, as well as improve local air quality and recreation.

Public and private interests in Colombia are avoiding some of the costs of more expensive urban water treatment plants by paying ranchers and farmers in mountain watersheds to be better stewards of their working lands, which provide drinking water to the country’s major cities.

As it builds out its low-carbon hydropower capacity to service its growing cities, China is thinking about where and how to build and manage its dams by evaluating the full value of a healthy Yangtze River for fish protein and flood protection to its communities.

As it plans for population expansion along the Thames Gateway, London has formed the East London Green Grid to look at how best to use natural infrastructure to reduce flooding and site future housing settlements.

More focused attention on natural infrastructure across regions, and by public and private sector leaders, will improve our ability to account for nature’s value, deepen our knowledge of how to deploy these solutions, and accelerate their uptake.

Global companies such as Dow, Shell and CH2M HILL are now working with organizations such as The Nature Conservancy to bring ecosystem science and engineering expertise together. Innovative partnerships such as the C40 Cities Climate Leadership Group and the Rockefeller Foundation’s 100 Resilient Cities provide platforms for the world’s cities to pool expertise and share knowledge on natural infrastructure solutions.

Last month, the Conservancy, C40 and the International Water Association published an Urban Water Blueprint that for the first time assesses the quality of urban watersheds for over 500 cities worldwide. We found that conservation investments in these watersheds—everything from better farming practices to forest protection—could improve water quality for more than 700 million people in 100 of the world’s largest cities and save roughly $900 million annually on water treatment costs.

Nearly 80 years ago, in the throes of the Great Depression and crippling drought, Roosevelt talked about the need to balance the budget of our natural resources, saying “The success of that form of budget balancing is just as important to the future of America as that of the Treasury.” FDR’s message still rings true.